Rust prevention process for sheet steel plating base

ABSTRACT

Process for producing plated sheet steel by coating a sheet steel plating base with an alkylimidazoline, forming an acid salt of the amine on the plating base by passing the coated plating base through an acid washing solution, and plating the resultant sheet steel, without any rinsing of the acid salt, by dipping in a molten metal bath. Also provided is an electroplating process wherein the acid salt of the amine is rinsed from the plating base prior to electroplating.

Matted States Patent 1 Shimada [4 1 Apr. 10, 1973 RUST PREVENTION PROCESS FOR SHEET STEEL PLATING BASE [75] Inventor: Shoji Shimada, Tobata-ku, Fu-

kuoka, Japan [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan [22] Filed: Jan. 25,1971 [21] Appl. No.: 109,646

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 729,127, May 14, 1968, abandoned, which is a continuation of Ser. No. 376,211, June 18, 1964, abandoned.

[52] US. Cl. ..1l7/5l, 117/114, 204/34, 148/6.l4, 106/14 [51] Int. Cl. ..C23c 1/04, C23c 1/02 [58] FieldofSearch ..117/51, 114; 252/390, 391, 392; 204/3234; 106/14;

[56] References Cited UNITED STATES PATENTS R23,227 5/1950 BlairJr ..252/390 X 2,333,206 11/1943 Sloan, ....1 17/127 X 2,533,048 12/1950 Rogers ..117/114 B X 2,748,066 5/1956 Whitehouse et a1 ..204/34 2,382,868 8/1945 Fink ..1 17/1 14 B X Primary ExaminerRalph S. Kendall Attorney-Wenderoth, Lind & Ponack [5 7] ABSTRACT 4 Claims, No Drawings RUST PREVENTION PROCESS FOR SHEET STEEL PLATING BASE This application is a continuation-in-part of Ser. No. 729,127, filed May 14, 1968, now abandoned, which in turn is a continuation application of Ser. No. 376,21 l, filed June 18, 1964, now abandoned.

This invention relates in general to a rust prevention process for a sheet steel plating base, and more particularly to a plating base intended for hot bath plating or electroplating, which has been kept in stock for a con siderable period of time before plating.

An object of this invention is to provide a rust prevention process for sheet steel to be plated, characterized' by coating either or both surfaces of the plating base to provide a long-lasting anticorrosive effect, and yet still permit easy plating, e.g., by tin or zinc.

Another object of the invention is to provide a rust prevention process for a sheet steel plating base, according to which one or more alkylimidazoline compounds are coated on the sheet steel base intended for either hot bath plating or electroplating.

A further object of this invention is to provide a sheet steel, to be plated, which is coated with an alkylimidazoline to provide a long-lasting anticorrosive effect, and which will permit easy tin or zinc plating as well as excellent paint attachability.

A still further object of this invention is to provide a rust prevention process for a sheet steel plating base, which will provide a protected plating base easy to handle, making it possible to use it on a field-to-field basis.

Another object of this invention is to provide a process for producing a plated sheet steel, characterized by subjecting the coated plating base to hot bath plating or electroplating after initially conducting a pre-treatment of the coated plating base.

Other objects together with a fuller understanding of this invention will be appreciated upon consideration of the disclosure given below.

It is known that there is a comparatively long interval between the last stage of sheet steel base manufacture and the plating of the sheet steel base, during which it is either in stock or in transport, in the form of a plating base. This invention is at least partially concerned with a rust prevention process for such a sheet steel plating base.

In the past, rust prevention of a sheet steel base plating intended for hot bath plating or electroplating has been attempted by application of oils. This results in many drawbacks, for example an increase in porosity or a surface defect in the base, unless a powerful degreasing process is employed. The resultant sheet steel base, therefore, cannot be used for coating. in order to solve this problem, there have been used such methods as the wrapping of the plating base in a dicyclohexylamine nitrite paper, or the spraying between plating bases of a powder of an evaporable, rust preventative agent of such an amine a compound. Compounds sprayed in this way, however, have a weak effect which does not last very long. MOreover, the spraying, as an application method, enables adjustment of the application volume of the rust preventative powder only with considerable difficulty, making it unsuitable for use on a field-to-field basis.

US. Pat. No. 2,533,048 to Rodgers, discloses a process of hot dip tinning steel sheets wherein the steel sheet is immersed in a pickling bath containing an inhibitor admixed therein, and then prior to the hot dip, the thus treated steel sheet is rinsed with water. Application of certain amines to ferrous metals to protect against corrosion is disclosed in U .8. Pat. Nov 2,333,206 to Sloan. if such ferrous metals coated with the amines as disclosed in the patent to Sloan were treated in accordance with the process of the Rodgers patent, the present inventors have determined that the acid salt which would be produced by immersion of the coated metal into the acid pickling bath would be removed by the subsequent water rinsing step. As will be apparent from the following discussion, the inventors have discovered that the acid salt produced on the plating base in accordance with the process of this invention is extremely useful in increasing the fluxing action during the hot bath plating.

This invention provides a new process which obviates the above-described defects. The use of the process of this invention provides an effective means of rust prevention, as follows.

Thus, the sheet steel plating base is coated with an alkylimidazoline compound on one or both surfaces of the plating base, or if desired, a mixture of alkylimidazoline compounds may be employed. These amine compounds may contain 4-19 carbon atoms, and preferably contain 10-14 carbon atoms. Thus, the alkylimidazoline compounds used in this invention may be represented by the formula where R is an alkyl group containing ll6 carbon atoms, preferably 7-l 1 carbon atoms.

The surface of the sheet steel plating base on which is formed a thin film of the alkylimidazoline is made ready for electroplating by passage through a bath of an acidic solution, containing for example hydrochloric or sulfuric acid, and subsequently rinsing the plating base with water to completely remove the acid salt formed by the acid treatment. In the event the plating base is to be subjected to hot bath plating, it is not necessary to remove the acid salt from the surface of the plating base, but rather, and in accordance with the present invention, the salt is left to remain on the surface of the plating base to provide an increased fluxing action during the hot bath plating.

The method of this invention comprises continuously coating a sheet steel plating base with a solution of a single or a mixture of alkylimidagoline CH (CH C H5N2 compounds containing less than 20 carbon atoms, using, for example, benzene or an alcohol as a solvent. It further comprises forming a film of the compound or compounds so applied. The resultant sheet steel plating base is useful for both hot bath plating and electroplating. In order to form a comparatively thin, even film, it is recommended to apply these compounds at the rate of 0.5-5 g/base box by using high voltage electrostatic oil application equipment. The compounds coated on the surface of the base will partially form their carbonates or bicarbonates when in contact with air while the base is kept in stock or is being transported, but these salts will not reduce or hinder the rust prevention effect. Such salts will be converted to, for example, the hydrochloride or sulphate salt in the course of the acidic washing.

Examples of the alkylimidazoline compounds are as follows:

2-propylimidazoline C H,C H N 2-butylimidazoline C H C H N Z-undecyliinidazoline C ll C l-l N 2-dodecylimidazoline C H C H N etc.

and isomers of these imidazolines.

The ability'of the plating base coated with each of these specific amines to undergo electric tin plating will be hereinunder explained. The plating base coated with each amine in an amount of 0.1 to 30 g/base box according to the electrostatic oil painting method using a high voltage of 10,000 to 100,000 volts, or by the spray method, was processed along an electric tin-plating line (1) immediately after, and (2) three months after the application of the coating, as specified in the following The result showedthat the tin plate thus electrically produced in either of the above-mentioned cases is not at all different,in, quality and yield, from that in the case of using the conventional uncoated base.

Forthe purpose of examining whether each anticorros'ive agent which might fail to be removed from the sheet steel plating base after having been passed through the electrolytic cleaning stage of the plating line hinders the succeeding pickling and electroplating, the pieces of sheet steel coated with each anticorrosive amine of the present invention in an amount of 0.1, 0.5 and 1.0 g/base box were tested, using a small-sized electric tin-plating apparatus. The testing conditions are as follows:

Pretreatment 5% HCl, at normal temp., for 2 sec.

Plating cell Circulation cell Plating solution Plating solution of ordinary electroplating line Temperature of plating solution 40C.

Current density 250 A/ft Flow speed of plating solution 300 f.p.m.

Amount of tin attached No. 20 and No. 160

. 6 The result of the test showed no impediment in either case of the products of Nos. 20 and 100, in terms of the amount of tin attached to the plating base.

5 yl)-imidazoline If sheet steel which can be prevented from rusting by being coated with an anticorrosive agent can be further coated with a paint without any problem in paint attachability, it will become possible to supply a rust-free painting base in the market, the significance of this being considered very great. Thus, the paint attachability of the cold-rolled sheet steel coated with each anticorrosive agent involved in the present invention in an amount of 0.1 to 5 g/base box was examined after the I sheet steel thus coated was painted with each of various light color paints (such as marketed denatured alkyd paint, thermo-setting vinyl paint, melamine alkyd paint, acrylic paint, phthalic acid paint, and epoxy paint) and then burned under corresponding conditions. The result showed almost no difference between the attachability of paint in this instance and that of the coldrolled sheet steel upon which no anticorrosive agent was coated. However, when the amount of each anticorrosive agent applied exceeded 5 g/base box, the attachability of paint was found to deteriorate with some paints.

It is desirable that the alkylimidazoline be well dehydrated when applied by means of the high voltage electrostatic oil application equipment. In this invention, only such alkylimidazoline compounds having less than 20 carbon atoms are used. Compounds having 20 or more carbon atoms decrease their melting point so that difficulty in application is increased when using them commercially.

EXAMPLE A sheet steel plating base was coated, by the spray method with 2-(1-ethylpentyl)-imidazoline kept at 60C at the rate of 0.2, 0.5, 1.0, 5 and 10 g/base box, respectively, and further directly coated with each of various marketed paints. The paint attachability was examined by a checkering test, drawing test, impact test, etc.

The result showed no difference in paint attachability between the base coated with 2-(lethylpentyl)- imidazoline in accordance with the present invention and the conventional uncoated sheet steel plating base.

Rust prevention capacity (determined by a stack test in the plant, that is, a test on the production of rust when the treated materials are stacked):

Application volume Rust produced after one month 2g/base box 15-30 spots/10x10 Laurylamine V.P.l. (vapor phase inhibitor bicyclohexylnmine nitrite 2-( l-ethylpentyl)- imidazoline 8g/hase box 2glbase box 3-13 spots/ 10x10 cm 1-6 spots/10x10 cm solvent at 20C):

10% 11,80. 10% HCI 2-( l-ethylpent- Easily soluble Mostly insoluble Easily soluble Mostly Laurylamine insoluble Surface tension Water 30C l7dyne/cm H 80 18C 74.1 dyne/cm 10% HCl 20C 72.25dyne/cm Removability after being coated on a steel sheet:

Boiling of the steel sheet in 5% NaOH for Sminutes Boiling of the steel sheet in 5% NaOH for 10 minutes 2-( 1-ethylpentyl)- imidazoline Laurylamine Y 2-( l-ethylpentyD- imidazole Laurylamine 10%-20% of the surface got wet with water l020% of the surface got wet with water Electro-tin-plating test:

the pretreatment was very low.

While the present invention has been specifically described and illustrated herein with reference to the preferred embodiments of the invention, it is to be understood that the present invention may be practiced otherwise than as specifically described and illustrated.

What is claimed is:

1. A process for producing plated sheet steel consisting essentially of continuously coating a sheet steel base with one or a mixture of alkylimidazoline compounds containing 4-19 carbon atoms, forming a fluxproducing, water-soluble amine salt on the sheet steel base by passing the thus coated sheet steel base through an acid washing solution and plating the thus treated sheet steel by dipping in a molten metal plating bath.

2. The process according to claim 1, wherein the alkylimidazoline compound contains 10-14 carbon atoms.

3. Plated sheet steel consisting essentially of a sheet steel base, at least one water-soluble alkylimidazoline salt containing 4-19 carbon atoms formed on the surface of the base and a metal superimposed on the salt.

4. The plated sheet steel of claim 3, wherein the alkylimidazoline salt contains 10-14 carbon atoms. 

2. The process according to claim 1, wherein the alkylimidazoline compound contains 10-14 carbon atoms.
 3. Plated sheet steel consisting essentially of a sheet steel base, at least one water-soluble alkylimidazoline salt containing 4-19 carbon atoms formed on the surface of the base and a metal superimposed on the salt.
 4. The plated sheet steel of claim 3, wherein the alkylimidazoline salt contains 10-14 carbon atoms. 